The Caspian Sea is the world's largest inland body of water, often classified as the world's largest lake or a full-fledged sea. It is an endorheic basin, meaning it has no natural outlets to the ocean, and lies between Europe and Asia. It is bordered by Russia, Kazakhstan, Turkmenistan, Iran, and Azerbaijan. The sea is saline, though only about one-third as salty as the ocean, with the northern part being nearly fresh water due to the inflow from the Volga River. The Caspian is famous for its sturgeon, which produce the world-renowned Beluga caviar. Beneath its floor lie some of the planet's most significant oil and natural gas reserves, which have led to complex legal disputes among the bordering nations regarding the division of the seabed. Geologically, it is a remnant of the ancient Tethys Ocean, which was cut off from the global ocean system millions of years ago.